McMaster Carr
Paul, I just went to the McMaster Carr web site to order. They have a
new page up on the Neoprene-Isolated rod ends which states the working
temperature is between 32ºF and 180º F. I don't think we can use
them. Jerry
I think they are just being overly conservative. The vast majority
of engine mounts in the world are neoprene. I had a discussion with
them about that concerning the temperature rating of the pressure gauges.
They lowered the temp rating on those too. These mounts are so overkill
it is ridiculous. They are basically covering their butts as far as
their warrantee is concerned. If you are still not happy with this
use a metal 3/8 on the lower oil pan end and a 1/2 inch rubber on the top
end. The cool end. Same left and right hand thread scheme.
I am going to stick with rubber on both ends.
Paul Lamar
Charlie Smith wrote:
No, they are not being overly conservative. Neoprene does not age very well in the presence of high temperature. It will harden quickly and eventually crack and break into pieces. This is also why 32°F is the low end for temperature. Either way, the spring rate goes up to the point to where you might just as well have metal there. If you must use Neoprene and have it placed near an exhaust pipe or manifold, please consider using a metal heat shield or inspect/replace often.
Charlie Smith
KIS Cruiser 4021
What type of rubber are they using for motor mounts Charlie?
Seems like all rubber turns to crap sooner or later.
I am not sure the rubber ball joint will run over 180 F anyway.
It is stuck out there on the back of the oil pan not near the exhaust.
True the oil can get over 200 F but the surface of the pan will
rapidly lose heat.
Well then use a steel ball joint on the lower end and
a rubber ball joint on the top end.
I'll still try it on the lower end and let people know what happens.
It won't be a catastrophic failure in any event and it is easily inspected.
Paul Lamar
Actually, yes. Eventually most any polymer will degrade from something. Every one has an Achilles heel. Most automotive motor mounts are made from natural rubber. The reason really is its glass transtiton temperature. It is around -60°C and that makes the mounts very effective in isolating vibration even at -40 degrees. The engineers are just very careful with the temps the mounts see. Some do have a mount installed in hot regions and there many engineers will use HNBR. Its extremely expensive and not likely to be available in commonly obtained hardware. If you can get it, EPDM may not be a bad choice. Its much more heat stable, has slightly better low temperature performance but it has no oil resistance. If you anticipate leaks of oil on it, it would be a bad choice.
If its possible to determine how hot the mount is getting, that's a good start for determining how long it will last. Neoprene's continuous use temperature is about 80-85°C [176 F to 185 F] meaning it can be expected to perform acceptably for about 2000 hours at that temperature. Hotter temps mean shorter life. A good rule of thumb is if the Neoprene part will last 2000 hrs at 80°C, then expect 1000 hours at 90°C, 500 hours at 100°C [212 F] and so forth. Keep in mind this is just a way to estimate useful life. You will reach a temperature where it will have zero hours of life and that point may not be readily apparent.
Just inspect often until you have confidence it looks OK. Be looking for cracks, crazing or chunks falling out (the usual rubber turning to goo things). Small radial cracks would be the way I would expect Neoprene to begin to fail.
Charlie Smith
KIS Cruiser 4021
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